US8038700B2 - System and method for dynamic skeletal stabilization - Google Patents

Abstract

There is disclosed a system and method for dynamic stabilization which provides for distraction of the inter-vertebral space while still allowing a patient a substantial range of motion. In one embodiment, an inter-vertebral dynamic brace is used to maintain proper distraction. The dynamic brace is designed to allow the vertebrae to which it is attached to move through their natural arc, maintaining the correct instantaneous center of rotation. An adjustable tensioning device is used to maintain the proper distraction and compression forces to restore and maintain proper kinematics, while allowing the dynamic brace to move through an arc centered with respect to the center of rotation of the portion of the spine between the vertebrae. In one embodiment, a method is provided for adjusting the dynamic brace both with respect to the center of rotation of the vertebrae in both the flexion/extension axis and in the superior/inferior axis.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the benefit of the filing date of, co-pending U.S. patent application Ser. No. 10/914,751 entitled “SYSTEM AND METHOD FOR DYNAMIC SKELETAL STABILIZATION”, filed Aug. 9, 2004. The present application is related to co-pending, and commonly assigned U.S. patent application Ser. No. 10/690,211, entitled “SYSTEM AND METHOD FOR STABILIZING INTERNAL STRUCTURES,” filed Oct. 21, 2003, the disclosure of which is hereby incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to skeletal stabilization and more particularly to systems and methods for stabilization of human spines and even more particularly to dynamic stabilization techniques.

BACKGROUND OF THE INVENTION

The skeletal system, particularly the human spine, is a complex structure designed to achieve a myriad of tasks, many of them of a complex kinematic nature. While performing its function, the spine must move into flexion (bending forward) and extension (bending backward). For example, the vertebrae that make up the lumbar region of the human spine move through roughly an arc of 15° relative to its neighbor vertebrae. Vertebrae of other regions of the human spine (e.g., the thoracic and cervical regions) have different ranges of movement. Thus, if one were to view the posterior edge of a healthy vertebrae one would observe that the edge moves through an arc of some degree (e.g., of about 15° if in the lumbar region) centered around an elliptical center of rotation. The inter-vertebral spacing in a healthy spine is maintained by a compressible disc which serves to allow the spine to move through this arc.

In situations (based upon injury or otherwise) where a disc is not functioning properly, the inter-vertebral disc tends to compress, and in doing so pressure is exerted on nerves extending from the spinal cord by this reduced inter-vertebral spacing. Various other types of nerve problems may be experienced in the spine, such as exiting nerve root compression in neural foramen, passing nerve root compression, and enervated annulus (where nerves grow into a cracked/compromised annulus, causing pain every time the disc/annulus is compressed), as examples. Many medical procedures have been devised to alleviate such nerve compression and the pain that results from nerve pressure. Many of these procedures revolve around attempts to prevent the vertebrae from moving too close to each other thereby maintaining space for the nerves to exit without being impinged upon by movements of the spine.

One such attempt is shown in U.S. Pat. No. 6,048,342 (hereinafter “the '342 patent”) in which screws are embedded in adjacent vertebrae pedicles and rigid spacers are then sewed between the screws. In such a situation, the pedicle screws (which are in effect extensions of the vertebrae) then press against the rigid spacer which serves to distract the degenerated disc space so as to prevent the vertebrae from compressing the nerves. This works for preventing nerve pressure due to extension of the spine, however when the patient then tries to bend forward (putting the spine in flexion) the posterior portions of at least two vertebrae are effectively tied together and thus can not move through any arc, let alone through 15° of motion desired for some regions of the spine. This not only limits the patient's movements but also places additional stress on other portions of the spine (typically, the stress placed on adjacent vertebrae being the worse), often leading to further complications at a later date.

In some approaches, such as shown in European Patent Publication 01/45,576 A1, a “stop” is placed between spinous processes and the spinous processes are then banded together. This procedure has the same limitations and drawbacks as discussed above for the '342 patent.

In still another attempt to solve the compression problem, a lever arm approach has been attempted, as shown in U.S. Pat. No. 6,290,700, again resulting in the same problems, namely, an effective “welding” of two vertebrae together.

United States Patent Application Publication No. US/2004/002708A1 (hereafter “the '708 publication”) with a Publication Date of Jan. 1, 2004 is entitled, “DYNAMIC FIXATION DEVICE AND METHOD OF USE” shows a dynamic fixation device that allows flexion. The device and method of the '708 publication uses a geometric shape to allow flexion but makes no provision for preventing or reducing disc compression during such flexion.

BRIEF SUMMARY OF THE INVENTION

There is disclosed a system and method for dynamic stabilization which provides for distraction of the inter-vertebral space while still allowing a patient a substantial range of motion. In one embodiment, an inter-vertebral dynamic brace is used to maintain proper distraction. The dynamic brace is designed to allow the vertebrae to which it is attached to move through its natural arc. An adjustable compression device is used to maintain the proper distraction force while allowing the dynamic brace to move through an arc centered with respect to the center of rotation of the portion of the spine between the distracted vertebrae. Accordingly, such dynamic brace aids in permitting a substantial range of motion in flexion, extension, and/or other desired types of spinal motion.

In one embodiment, a method is provided for adjusting the dynamic brace, both with respect to the center of rotation of the distracted vertebrae in both the flexion/extension axis and in the superior/inferior axis.

In a still further embodiment, the spring tension is adjustable on a patient by patient basis to take into account body weight and strength as well as physical characteristics of the patient's skeletal system. Also, provisions may be made to convert the dynamic brace to a static brace while the device remains in situ.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows one embodiment of a dynamic brace fitted between a pair of bone anchors;

FIGS. 2A,2B and2C show one embodiment of a dynamic brace fitted between adjacent spinous processes;

FIGS. 3A,3B and3C show one embodiment of a dynamic brace used for spinous process stabilization;

FIGS. 4A,4B and4C show one embodiment of a dynamic brace used for pedicle screw stabilization;

FIGS. 5A and 5B illustrate the movement of the center of rotation between a pair of adjacent vertebrae;

FIGS. 6A,6B,6C,6D,6E and6F show one embodiment of a procedure for implanting a dynamic brace to implanted pedicle screws;

FIG. 7 shows one embodiment of a dynamic stabilization device having a cover thereon; and

FIGS. 8A and 8B show one embodiment of a cross-connector between a pair of dynamic braces.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows dynamic brace (or “rod”)40 positioned with respect topedicle screws101 and102 insystem10. This is but one embodiment of the manner in which a dynamic stabilization device can be employed to partially off-load (or un-weight) the disc between vertebrae (to reduce compression forces) so that as the spine moves through its normal range of motion pressure on the disc is reduced throughout the entire range of motion. In this embodiment, the pedicle screws are positioned in the pedicles of the spine as discussed and shown in the above-identified co-pending U.S. patent application entitled “SYSTEM AND METHOD FOR STABILIZING INTERNAL STRUCTURES.”FIGS. 6A through 6F discussed below show in more detail how and where the pedicle screws are implanted for a dynamic brace in accordance with one procedure.

As will be discussed, one of the purposes of the dynamic brace is so that as adjacent pedicles move with respect to each other they are free to follow their natural motion around a center of rotation. In certain embodiments, some amount of translation is permitted such that the center of rotation need not be a fixed point. As shown inFIG. 1,brace portions41 and43 ofdynamic brace40 are free to move with respect to each other along their longitude axis in a telescoping manner. This motion is controlled, in part, byspring44.Stop46, working in conjunction withstop45, serves to allow spring44 (or springs) to be effectively lengthened or shortened thereby changing the force the spring exerts which, in turn, changes the force betweenbrace portions41 and43. The relative movement betweenbrace portions41 and43, which could be a tube within a tube, allows for 5° to 20° flexion of the vertebrae to which it is attached in certain embodiments. Of course, the implementation ofbrace40 may be adapted to allow for any desired range of flexion in alternative embodiments. In addition, as will be detailed,dynamic brace40, as it bends, will maintain a correct biomechanical center of rotation, which is not necessarily limited to a fixed center of rotation, with respect to the vertebrae while also reducing or eliminating pressure on the disc between the vertebrae. This partial off-loading of the disc is accomplished by the rigid nature of the rod and spring assembly. While various embodiments are described herein as employing a spring for achieving the permissible degree of movement in the brace, other devices will be readily recognized for substituting for this function, such as employing a hydraulic, pneumatic or other distracting system. If rotation of the device becomes an issue, the telescoping portions can be designed, for example, using an interlocking groove or using matched longitudinal channels, one in each tube, to prevent relative rotation.

Also, as will be seen, by changing the position wherehead12grips portion41, the center of rotation in a superior/inferior axis of rotation along the patient's skeletal anatomy can be adjusted.Dynamic brace40 can be adjusted to create a proper distraction height prior to being implanted and thereafter can be adjusted to the desired distraction force in situ. Because the spine is free (subject to constrained motion) to bend, multiple dynamic braces can be used along the spine while still allowing the spine to move into flexion and, if desired, extension. In certain procedures, thedynamic brace40 may be, for example, be positioned and correctly tensioned/adjusted in communication with a device that determines a patient's spinal neutral zone.

FIGS. 2A to 2C show a dynamic stabilization device being used across adjacent spinous processes21-SP-22-SP as opposed to being in the pedicles, such as in pedicle22-P and pedicle21-P.FIG. 2A shows twovertebrae21 and22 (which could, for example, be L4, L5 or any other vertebrae) separated bydisc23.Space204 betweenvertebrae21 and22 is where nerves would typically emerge from the spinal column.FIG. 2A shows the skeletal system in the neutral position. In this position, the angle between the generally horizontal planes defined by end-plates of the adjacent vertebrae could be, for example, 8°. Note that, while not shown, an extension (or a stabilization device30) could extend to a next adjacent spinous process if multiple vertebrae are to be stabilized. The center of rotation for this vertebral pair is210. Note that while this embodiment is shown as a mated pair, it can be used unilaterally. Also note that the attachment to the spinous process should be as anterior on the spinous process as practical. The junction of the lamina and the spinous process would be a strong fixation point.

FIG. 2B shows thedynamic stabilization device30 withvertebrae21 and22 in the flexed position. Note that in the illustration spinous process21-SP has moved up and into the right (anterior) as the spine is bent forward (flexion). A typical movement distance for the posterior of the spinous process is patient specific and would be approximately 4-16 mm.Spring34 has expanded along with the dynamic brace to allow spinous process21-SP to move upward and forward rotating about center ofrotation210. As will be discussed hereinafter, the center of rotation is not a constant point but will move in an ellipse or centroid as the vertebrae move from extension to flexion.

When fully in flexion, the front surfaces ofvertebrae21 and22 form an angle of, for example, −4°, which is a change of 12° from the neutral position. Assuming the vertebrae goes into extension by, for example, 3°, the total range of motion is about 15° as shown inFIG. 2C. Ideally, the center of rotation would be around the location shown as210. The center of rotation of the spine does not change from flexion to extension or with side bending. However, the “Instantaneous Axis of Rotation” (IAR) changes throughout the rotation arc. The sum of all of the IARs is therefore one point which is called the Center of Rotation “COR). When the spine moves through flexion and extension the motion of the adjacent vertebrae can be an arc defined by 5 points as shown. The dynamic brace can be adjusted to move the center ofrotation210 forward-backward (X axis) and upward-downward (Y axis), as will be discussed.

InFIG. 2B,spring34 serves to pull the spinous process back together thereby limiting the compression applied to nerves extending from204. Note that as betweenFIGS. 2A and 2B the respective pedicles have separated by approximately 8 mm. The range shown (31 mm to 39 mm) is but one example. Other patients would have other starting and ending points depending upon their particular physical structure and medical condition. The important point being that the pedicles (vertebrae) and facets can move through their natural range of motion and thus separate during flexion.

InFIG. 2C,spring34 serves to stabilize the spine when in extension. In both cases, the limit of movement is controlled by the limits ofbrace portions31 and33 along their longitudinal length.

FIG. 3A shows a cross-section of the one embodiment of spinous processdynamic device30 having an external spring and a pair ofexpandable brace portions31 and33.Portion31, which can be a solid rod, if desired, (or any other suitable structure, such as a tube, a plurality of parallel-arranged rods or tubes, etc.) moves insideportion33 which can be a hollow tube. External of both of these portions isspring34, the tension of which is controlled bystop36 tightening (or loosening) under control of openings301 (FIG. 3B).Stop36 in this embodiment works in cooperation withthreads306. Note that any type of stop can be used, thread or threadless and the stop(s) can be inside the rod or outside. Dynamic stabilization device (or “brace” or “rod”)30 can be attached to either side of the spinous process or could be used in pairs interconnected by rod312 (FIG. 3C).

As shown inFIG. 3A, as the spinous process moves into flexion,brace portion33 moves upward.Brace portion31 remain relatively stationary and thus rod end31-2 moves down (relatively) insideportion33. This expansion and contraction along the lateral length ofdevice30 allows the spine to follow a normal physiologic motion during bending of the spine.

Forward, lateral and twisting motion ofdevice30 are accomplished byspherical bearing311 which is free to move in three planes or axis aroundspherical end support312.

Stop36 is moved to adjust tension orspring34—as it is moved upward (toward stop35) force increases and as it moves downward force decreases. Force marks (e.g., triangles andsquares307 shown in this example) embossed (or otherwise marked) onshaft31 aid the surgeon in adjustment of the spring force. Thus, for instance, if the triangles are showing the spring force could be, for example, 30 pounds and if the squares are showing the spring force is known to be, for example, 60 pounds. This pre-calibration helps the installation process. Note that the spacing between these force marks in the drawing are arbitrarily drawn in this example, but may be implemented so as to represent the difference between forces.

Load transfer plates304 help distribute the forces between the respective vertebrae.Spikes310 can be used for better load distribution to the spinous process.

FIG. 3B showsdevice30 from a perspective view.Bearings311, ofdynamic stabilization device30, revolve aroundrod end bearings312 and allow rotation of the brace for flexion/extension; lateral bending and trunk rotation.Fastener305 serves to hold the brace to the end support.

FIG. 3C shows one embodiment of a pair of dynamic stabilization devices connected on either side of spinous process21-SP (22-SP).Device30 is installed by creating a hole (by drilling or other means) in each spinous process and screwing (or otherwise connecting)rod312 through the created hole to interconnect the two internally separated devices, as shown.

FIG. 4A shows another example embodiment of adynamic stabilization device40 for use between bone anchors, such as, for example, pedicle screws.Device40 is constructed similar todevice30 except that the ends are held in position by pedicle screws.Portion47 is attached to one pedicle screw whileportion41 is held by a second pedicle screw. Adjustment along the Y-axis is achieved by moving the position alongportion41 where the pedicle anchor is clamped todevice40. This effectively changes the neutral length ofdevice40.

FIG. 4B showsdevice40 extended when the spine is in flexion.Device40 extends around a curvilinear path (as will be detailed with respect toFIG. 4C) and the spring length increases, in this example, from approximately 0.745 to 0.900 inches. Spring deflection is 0.155 inches.End48 ofdevice41 is assumed in a fixed position whileend47 moves superior (right) and exterior (down) with respect to end48. Of course, other dimensions of increase in length and deflection may be achieved in other uses. That is, different amounts of flexion and extension may be permitted in certain patients.

FIG. 4C showsdevice40 attached to pediclescrews101 and102. One end ofportion41 is held captive byhead12 positioned at the top ofpedicle screw102 by a polyaxial connection.Portion43 ofdynamic stabilization device40 slides over curved guide portion41-1 ofportion41. In this embodiment, portion41 (and41-1) can be hollow or solid andportion43 will be hollow. End43-1 ofportion43 is held captive byhead11 polyaxially mounted to pedicle screw (or other type of bone anchor)101. Note that end43-1 may be adjusted to extend beyondhead11 prior to being clamped intohead11 if it is necessary to allow for a greater range of travel of end41-1 withintube43. For example, this may be necessary for closely placed bone anchors. As discussed,spring44 is positioned around the outside ofportion43 betweenstops45 and46.Spring44 is held in compression and adjusted byrotatable stop45 moving under control ofthreads406.

As discussed, guide41-1 fits inside ofportion43 and is curved. It is this curve that allowspedicle screw101 to move in an arc (as shown) when the pedicle to whichscrew101 is attached rotates in flexion. This allowsdynamic stabilization device40 to rotate about center ofrotation210 with a natural motion. Natural meaning how the spine would have moved had it been working properly. Note that the X-axis center of rotation ofdevice40 is controlled by the bend of guide41-1 relative toportion43. As discussed above, the center of rotation in the superior/inferior axis (Y-axis) is controlled by the position ofend48 with respect to thepedicle screw102.

Positions101-1 and101-2 ofpedicel screw101 shows pedicle screw kinematic analysis as the spine moves into flexion. As shown,pedicle screw101 goes through a range of arc motion around center ofrotation210. It is this range of arc motion that the stabilization device tries to maintain.

FIG. 5A showsdynamic stabilization device40 positioned in pedicles21-P,22-P ofvertebrae21,22, respectively. The length of the device betweenheads11 and12 is adjusted during implantation such that dimension H positions the length by tighteninglocks66 when the H dimension is as desired. This, as discussed, is the (Y) axis (or superior/inferior) of adjustment. The curvilinear motion is set with respect to the R dimension and this is the (X) axis (or flexion/extension) of adjustment. The (X) and (Y) dimensions are set with reference to the desired center ofrotation210. The force provided byspring44 in combination withportions41 and43 keepvertebrae21 from pressing too heavily ondisc23 thereby partially off-loading the intervertebral disc.

FIG. 5B shows that by applying a moment aboutextensions55 and then locking down the length ofdevice40 there can be created an anterior distraction force onvertebral bodies21,22. This will more evenly distribute the loading ondisc23 thereby creating a more optimal environment for the disc when compared to only a posterior distracting implant system.Extensions55 are removed after the proper length ofdevice40 is achieved.

FIGS. 6A-6F show one procedure to insert the dynamic brace between vertebrae, such as vertebrae L5 (21) and L4 (22). This procedure is detailed in the above-identified patent application and is repeated herein for convenience. The surgeon identifies the desired vertebral levels and pedicle positions via standard techniques. Once the target vertebrae are identified, a small incision is made through the skin and a tracking needle (or other device) is inserted to pinpoint exactly where each anchor is to be placed. A fluoroscope, or other x-ray technique, is used to properly position the tracking needle. Once the proper position is located, guide wire (K wire)622 (FIG. 6A) is positioned with its distal end against the pedicle, in this case pedicle636-1 of vertebrae L5. Aguide wire623 may be similarly positioned with its distal end against/within pedicle637-1 of vertebrae L4.

As shown inFIG. 6B the surgeon then slides a series of continuing largersized dilators612,612a,612b,612cdownguide wire622, and slides a series of continuing largersized dilators613,613a,613b,613cdownwire623.

Approximately four or five dilators are used until a diameter suitable for passing the anchor and its extensions is achieved. A tap is inserted over the K wire to tap a hole into the pedicle in preparation for receiving the anchor, which in this case is a pedicle screw. This tap will usually be a size slightly smaller than the pedicle screw thread size selected for that patient and that level.

After the hole is tapped and the K wire and the inner dilators, such asdilators613,613a,613b, are removed, the surgeon is ready to introduce the anchor into the vertebrae. As shown inFIG. 6C, prior to inserting the anchor (e.g., pedicle screw),dynamic brace40 is attached to screw101 to form a brace-screw assembly. This assembly is then positioned at the distal end ofcannula65 and a screwdriver or wrench is inserted intocannula65 and attached toproximal end61 ofdynamic brace40. The entire assembly is then inserted into dilator613C. The screwdriver engages withproximal end61 ofdynamic brace40 so as to allow the surgeon to screwpedicle screw101 into the pre-tapped hole in vertebrae L4. Pressure on the screwdriver forces the screw to be in-line with the dynamic brace, which, in turn, is in-line with the screwdriver. The screwdriver can be removeably attached to end61 ofdynamic brace40 by engaging, for example, a flat and/or hole in the brace end.

This same procedure would be repeated for each additional level, in this case level L5, except thatscrew102 has assembly12 affixed thereto.Assembly12 is adapted to receiveproximal end61 ofdynamic brace40 as will be more fully described herein.

For a single level the above procedure is typically performed first on one side of both vertebral levels and then on the other side. When finished, four pedicle screws are inserted, holding two dynamic braces positioned laterally with respect to the center of the spine.

Once both screws are in place in vertebrae L4 and L5, dilators612C and613C are removed and, the surgeon slides a blunt dissection tool into the incision and gently parts the muscle bundle below the skin (or cuts a slit in the skin if necessary) between vertebrae. Alternatively, the blunt dissection tool could go down the second cannula and, starting at the bottom of the second cannula work open the muscle bundle between the cannula working upward as far as is necessary. Using this procedure, the muscles (and other tissue), only need be separated to a point where thedynamic brace40 must pass. Thus, the separation need not go to the skin level. This reduces trauma even further.

Once an opening in the muscles (or in the skin if desired) has been developed betweencannulas64 and65,dynamic brace40 is then positioned, by pivoting, as shown inFIG. 6D, by sliding a tool downcannula65 to engageproximal end61 ofdynamic brace40. The tool could have a force fit withend61 or a handle for controlling removable attachment withdynamic brace40. Once the tool is mated withend61 ofdynamic brace40 the surgeon can pull the tool slightly outward to disengage brace end43-1 fromscrew101.Brace end61 is forced out of cannula65 (through opening65-1 thereof) and through the prepared muscle opening and into opening64-1 ofcannula64. Once withincannula64, the surgeon, manipulatesbrace end61 downcannula64 and into a mating relationship withscrew102. Once this mating relationship is achieved, the tool is released frombrace end61 and the tool is removed from both cannulas.

The surgeon receives positive feedback (a sensory event), either by feel (for example, a snap action) or by sound (for example, a click), or both whendynamic brace40 is properly mated withassembly12. If desired, one or both ofassembly12 or11 mounted to the respective pedicle screws102 and101 can be angularity adjusted to accommodate the patient's body structure. The polyaxial nature ofassemblies102 and101 with respect to the anchors allows for such adjustments which are necessary for a variety of reasons, one of which is that the angulation between adjacent vertebral pedicles varies.

As shown inFIG. 6E, after all angular and lateral adjustments are made, setscrews66, or other locking devices, are introduced downcannulas64 and65 to lock each end ofdynamic brace40 to its respective pedicle screw. As discussed above, this establishes the y-axis adjustment of the dynamic brace.

As shown inFIG. 6F, once the proximal end ofdynamic brace40 is snapped in place to screw102 and setscrews66 are tightened,cannulas64 and65 can be removed and the incision closed.

FIG. 7 showsalternative embodiment70 of a dynamic stabilizationdevice having cover77 surrounding spring74. In this embodiment, the ends ofcover77 are held tostops75 and76 byrings79 fitted intoslots78. The cover is used to protect the device from being interfered with once implanted. Cover (or sleeve)77 can be constructed from fabric and/or polyester, as examples.

FIG. 8A shows a pair ofdevices40 interconnect with one ormore cross-connectors81. The cross-connectors can be fixed or adjustable, and straight or curved as desired, and could be a bar or plate or a tube as shown. The cross-connector acts to combine individual dynamic stability, has devices into a single assembly and will serve to provide a more fluid motion. The cross-connects can be individual, as shown inFIG. 8B with openings to ends82 and83 to go aroundmembers41,42 ordevice40 or the entire unit can be constructed as a unit, if desired

Note that in any of the embodiments shown, the spring force can be increased to a point where the device effectively becomes static in order to achieve fusion. Also, one or more holes could be positioned through the slide portions such that when a pin is inserted through the holes, the pin effectively prevents the brace from further expansion or contracting. For example, with reference toFIG. 3A, pin330 could be pushed throughholes331 and332, inportions31 and33. The pin could, for example, have spring loaded balls (or any other mechanism) that serve to prevent the pin from easily pulling out ofdevice30 once inserted. In addition, thespacing stop36 could be tightened, either permanently or on a temporary basis, to a point where spring tension effectively places the device in a static condition in order to promote fusion of the treated vertebrae in situations where motion preservation fails to meet surgical end-goals.

Note also that with this device it is possible to take neutral zone displacement readings so as to be able to tension the device properly with respect to a patient. Based on the readings, both the X and Y axis can be adjusted. A dynamic stabilization system should be sensitive to proper placement of the device to restore proper kinematics and full range of motion, and avoid causal deleterious effects of increasing rate of degeneration on adjacent segments. A neutral zone device is a device that can aid in the placement of the dynamic stabilization device by determining the center of rotation in flexion/extension. Once this center of rotation has been determined, the device can be located to best reproduce that center of rotation. The neutral zone device will cycle the spine through a range of motion measuring forces throughout the range of motion. Also, the device can be used after device implantation to confirm proper implant placement.

The curvilinear guides discussed herein reproduce the natural motion of the spine while still. As shown herein, a pair of curvilinear guides (one female and one male) is used to create a curvilinear path of the pedicles which creates, restores and controls the normal center of rotation. Other embodiments that would produce the proper motion could include; for example:

• • a) a guide bar comprising a pair of pins articulating in a matching pair slots where the slots would diverge to produce a curvilinear motion of a point on the guide bar;
  • b) a pair of curvilinear plates with attachment means for bone anchors;
  • c) any type of curvilinear guides made up of male and female shapes following a curvilinear path with a geometric cross section (i.e. dovetail, T-slot, round, square, rectangle, etc. cross section geometry);
  • d) a four or five bar mechanism that would produce a curvilinear path of the pedicle screw.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims (19)

1. A dynamic spine stabilization system comprising:

a first pedicle screw having a first proximal end portion and a first distal threaded portion;

a second pedicle screw having a second proximal end portion and a second distal threaded portion;

a dynamic brace including:

a first brace portion having a curvilinear guide portion;

a second brace portion having a aperture with a curvilinear interior surface, the aperture sized to receive the curvilinear guide portion, wherein the first and second brace portions are movably coupled to one another along a curved path having a center of rotation about which the first and second brace portions slide relative to each other;

a first end portion coupled to the first brace portion and to the first proximal end portion of the first pedicle screw;

a second end portion coupled to the second brace portion and to the second proximal end portion of the second pedicle screw;

a biasing member coupled to the first and second brace portions when the first and second brace portions are at a first predetermined position along the curved path which provides a force to the first and second brace portions at the first predetermined position; and

a threaded stop coupled to the biasing member to adjust the force provided by the biasing member.

2. The dynamic spine stabilization system ofclaim 1, wherein the biasing member is a helical spring, and at a second predetermined position along the curved path, the helical spring is coupled only to either the first brace portion or the second brace portion; and wherein the first end portion is a first rod member and the second end portion is a second rod member.

3. The dynamic spine stabilization system ofclaim 1, wherein the biasing member is an elastomeric sleeve.

4. The dynamic spine stabilization system ofclaim 1, wherein the threaded stop is coupled to the first brace portion.

5. The dynamic spine stabilization system ofclaim 1, further comprising a second stop coupled to the second brace portion.

6. The dynamic spine stabilization system ofclaim 1, wherein the threaded stop is longitudinally adjustable relative to the first brace portion member.

7. The dynamic spine stabilization system ofclaim 1, wherein the dynamic brace is longitudinally adjustable relative to the first pedicle screw.

8. The dynamic spine stabilization system ofclaim 1, wherein the first end portion is polyaxially coupled to the first proximal end portion of the first pedicle screw.

9. A dynamic spine stabilization system comprising:

a first pedicle screw having a first proximal end portion and a first distal threaded portion;

a second pedicle screw having a second proximal end portion and a second distal threaded portion;

a dynamic stabilization device including:

a first component having an articulating portion with an arcuate shape;

a second component having a longitudinal cavity with a least one arcuate wall, wherein the first and second components are movably coupled to one another along an arcuate path partially defined by the arcuate wall and having a point of rotation about which the first and second components articulate;

a first rod member connected to the first component and coupled to the first proximal end portion of the first pedicle screw;

a second rod member connected to the second component and polyaxially coupled to the second proximal end portion of the second pedicle screw;

a resistive element coupled to the first and second components when the first and second components are at a first predetermined position along the arcuate path which provides a resistance to the first and second components when at the first predetermined position and at a second predetermined position along the curved path, the resistive element is coupled only to either the first or the second components; and

a threaded member coupled to the resistive element wherein the threaded member is positionally adjustable relative to the first and second components.

10. The dynamic spine stabilization system ofclaim 9, wherein the resistive element is a spring.

11. The dynamic spine stabilization system ofclaim 9, further comprising a first set screw coupled to the first rod member and fixing a first angle of the first rod member relative to the first pedicle screw.

12. The dynamic spine stabilization system ofclaim 9, further comprising a second set screw coupled to the second rod member and fixing a second angle of the second cylindrical end portion relative to the second pedicle screw.

13. A dynamic spine stabilization system comprising:

a first pedicle screw having a first proximal end portion and a first distal threaded portion;

a second pedicle screw having a second proximal end portion and a second distal threaded portion;

a dynamic stabilization device including:

a first component having an articulating portion with an arcuate shape;

a second component having a longitudinal cavity with a least one arcuate wall sized to receive the articulating portion, wherein the first and second components are movably coupled to one another along an arcuate path partially defined by the arcuate wall and having a point of rotation about which the first and second components articulate;

a first cylindrical element coupled to the first component and to the first proximal end portion of the first pedicle screw;

a second cylindrical element coupled to the second component and to the second proximal end portion of the second pedicle screw;

a resistive element coupled to the first and second components when the first and second components are at a first predetermined position along the arcuate path which provides a resistance to the first and second components at the first predetermined position; and

a threaded member coupled to the resistive element and positionally adjustable relative to the first and second components.

14. The dynamic spine stabilization system ofclaim 13, wherein at a second predetermined position along the curved path, the resistive element is coupled only to either the first component or the second component.

15. The dynamic spine stabilization system ofclaim 13, wherein the resistive element is a spring.

16. The dynamic spine stabilization system ofclaim 13, wherein the first cylindrical element is polyaxially coupled to the first proximal end portion the first pedicle screw.

17. The dynamic spine stabilization system ofclaim 13, further comprising a first set screw fixing a first angle of the first cylindrical element relative to the first pedicle screw.

18. The dynamic spine stabilization system ofclaim 13, wherein the second cylindrical element is polyaxially coupled to the second proximal end portion of the second pedicle screw.

19. The dynamic spine stabilization system ofclaim 13, further comprising a second set screw fixing a second angle of the second cylindrical element relative to the second pedicle screw.

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